Not enough hot water, boiler short cycles, what to do?

gat

The house has 3 stories. Originally the whole house was on one zone, and the 2nd and 3rd floors would get too hot. We had it re-zoned to 3 different zones, one for the kitchen (which was completely rebuilt), one for the other 3 rooms on the 1st floor, and one zone for the entire 2nd and 3rd floors. This has greatly improved the comfort level, but now the 2nd/3rd floor zone is only needed on particularly cold days; usually only the two 1st floor zones are needed, and that is what's most likely causing the short cycling.

To specifically answer your question, most of the house has radiators, except for the kitchen which is new and has one section of finned tubed baseboard plus one under-cabinet unit with a blower.

On those really cold days we get a few times per winter, the boiler runs almost constantly, so I wouldn't consider it undersized -- at least given the questionable insulation of our house, which is something we will also address.

gat

We live near Boston in a 3500 square foot old victorian. We have a Burnham V-77 oil boiler with 3 heating zones. Our hot water is a separate gas hot water heater, and it's too small to fill our new 80 gallon tub. The boiler also only burns for 2 minutes at a time typically when it's not too cold and only the first floor zone needs heat, which I am told is inefficient.

Another interesting tidbit is that the boiler has a tankless coil. The hot water used to be teed through both the tankless and the gas hot water heater in parallel, but in that configuration we noticed occasional rust in our hot water, the hot water temperature would fluctuate a lot, and we would get hot water coming out of our cold water faucets at times! Clearly this is _not_ the correct way to hook this stuff up! We shut off the cold water inlet valve to the tankless coil (but left the outlet valve open to prevent pressure buildup), so all of the hot water now comes from the gas hot water heater, and the problems with hot water coming out of the cold and the rust have gone away, but we are left with not enough hot water capacity.

What would folks recommend? Just install a larger gas hot water heater, which is probably the cheapest option? Switch to an indirect hot water heater; is that a reasonable option without replacing the boiler at the same time? What about an Ergomax indirect water heater which claims to act as a buffer to reduce short cycling, and would provide our hot water too? Should I look into adding smarter controls to reduce the short cycling?

Weezbo

Hire someone in your area to come to your home

and "cop a visual"

then the correct pieces will be placed in the system and bought up to code should you then hire them to make the required changes. *~/:)

try clicking on Find a professional on the top of this page.

jp_2

on demand?

this may be a good situtation for an on-demand gas water heater. where you occasionally what large amounts of hot water, but for the most part, smaller amounts.

why store 80 gallons of hot water if you only want that amount twice a week?

ALH_4

water heater

It sounds to me like the heating system could use an overall evaluation, as Weezbo already stated.

In my opinion, the best option is to add an indirect off your boiler and get rid of the gas water heater. You do not necessarily need to replace your boiler at the same time if it is functioning properly and is in good condition. Your boiler may be oversized. It would not hurt to check the heat loss of the home against the output of the boiler. There is a Heat Loss Calcs link at the top of this page that will allow you to do this yourself if you like. It is always best to start from the beginning, and the heat loss estimation is the beginning.

Another option is to put a solar collector on your roof and add solar domestic hot water preheat ahead of your gas water heater, but the capacity would vary some depending on the available sunlight. Not the least expensive option, but probably the most environmentally friendly, and it may even make financial sense in the long run.

gat

Thanks for the input. I'm bringing in a heating contractor to take a look at our system, and I'll follow up with another post after that.

J.C.A._3

2 things I would check.

#1, Make sure the control for the old tankless was set down low and...

#2, If the finances are available...look into the Turbomax "reverse indirect" as an alternative.

This beauty makes COPIOUS amounts of hot water...when sized properly and can ALSO act as a buffer for that pesky short cycling problem.

Think of it as a REALLY high capacity tankless.You can use the existing control to maintain some boiler temp.(above condensation point , say 5 or 10° above wanted water temp...to help keep the chimney warm) as a sort of "stand-by"...which will boost the tanks ability to make enough hot water to MORE than fill the bath tub.

I can't say enough about this product...yet. The 2 that I've installed have far surpassed any expectations and when that is figured in, I don't find the price point to be such a deterrent.

Check it out and be amazed. BTW...the manual is a bit pessimistic...IMHO. Chris

ALH_4

reverse vs. standard indirect

Wouldn't an 80-gallon reverse indirect contain the same amount of heat as an 80-gallon standard indirect? The heat capacity of the 80 gallons is the same in each case. Have they improved the insulation on the Turbomax tanks? The fiberglass wrap they were using was a little sub-par in my opinion.

I believe that heat exchanger surface area is the defining characteristic for an indirect water heater, whether reverse or standard.

How does a reverse indirect provide better performance than a standard indirect?

J.C.A._3

Andrew,

I too was surprized.

Look at the charts provided by Turbomax, and you'll see that a 23 gallon unit, with the right temp. rise and boiler feed temp.will perform JUST as well as the larger size. I'm at a loss for the proper explanation. I DO believe that the larger units DO have more and taller coils.

I've installed 1 in a restaurant...and one in a Church. The Church has a baptismal that is almost 1500 gals., and the pastor told me he had to dump and reheat some of the tank on Easter Sunday....as the water was "getting cool", and their call was for 40° water to be raised to minimum 85°. A 23 gallon unit passed the audition with colors!

Looking at a cut-a-way at the recent PHCC show in Ma., I was pretty sure that the transfer coils were quite a bit larger (in total) than any indirect coil I've looked at lately. Thinner, yes but much bigger...and the cold going through them would seem to keep them from "liming" in almost any situation like some coils that use "finned exchange surfaces" would.

The insulation appeared to be on par with most indirects...to me anyway.

I hope I made the case. I'm honestly just reporting what I've been fed so far. Chris

gat

So I had a guy come out to take a look at the system. To improve the system efficiency he recommended adding an outdoor reset control, and also recommended operating the boiler in cold start mode instead of using a low limit of 140. I asked about the HeatManager product; he claimed it works, but not as well as an outdoor reset. I'm not sure he was too familiar with HeatManager.

Also he recommended an indirect water heater (viessman was his top recommendation, superstor 2nd) on a separate zone with its own circulator.

This all sounds fine to me, but I'm wondering if it really addresses the short cycling, and if using cold start mode is likely to damage the boiler?

J.C.A._3

Gat,

If that puppy's been warm since the day it was installed...I wouldn't even consider changing it to cold start. Maintain a lower temp., say 120°. This will keep all that has been warm, still warm and avoid the different shrinking rates of the various materials involved.

Either of the indirects suggested are fine products, but their heatlosses are the reason for maintaining some temperature. 1/2 a degree an hour with a boiler set up for cold start could conceivably make a boiler NOT run for 20 or more hours, if noone uses any hot water.(standard differential of any honeywell control is 10-12°)

I like the indirect move, but not the cold start choice.Chris

Radiant Wizard

I have a question

Before I even want to anwser your question...What's the heat load the boiler is trying to satisfy? What I mean by this is, How many feet of baseboard is in the home? Is it cast iron or finned tubed? If not baseboard then do you have radiators. By your thread I'm thinking either the boiler is too big to start and the location of the thermostat is being satisfied to quick (meaning the the btu output of the heat emmitters is much more than the room requires)

gat

I couldn't tell you what the previous owners did, but we have shut off the unit for the summer three times. But I suppose a seasonal shutoff is quite different from having the unit drop to room temperature and then climb back up to 160-180 on a regular basis.